1. Technical Field
The present invention relates to a planar light source device used in an image display device such as a liquid crystal display device and a liquid crystal display device using the same.
2. Description of the Related Art
In a related planar light source device, for example a planar light source device for a non-spontaneous light-emitting display device such as a liquid crystal display device, a side light type (also called an edge light type) and a direct type are known. The side-light-type planar light source device has a structure in which a light source is disposed on a side surface portion of a mold frame included in a rear frame. The direct-type planar light source device has a structure in which a light source is disposed on a rear surface of a mold frame facing a display unit.
Further, in the side-light-type planar light source device, a light guiding plate is provided to guide the light emitted from the light source to a desired direction, and the light emitted from the light source, for example a line light source such as a cold cathode fluorescent lamp (hereinafter, referred to as a CCFL) or a point light source such as a light emitting diode (hereinafter, referred to as an LED), is reflected inside the light guiding plate. And then, the light is diffused by a diffusion pattern provided inside the light guiding plate, and the light is emitted to the light emission surface. When the light guiding plate is provided, a display panel such as a liquid crystal panel is provided on the display surface side of the light guiding plate. A front frame having an opening and supporting the display panel, a mold frame, and a rear frame are disposed on the display surface side of the display panel.
Furthermore, in order to efficiently emit the light emitted from the light source to the display panel, an optical sheet, for example a prism sheet for improving regularity or a reflection sheet for reflecting the light toward the light guiding plate or the display panel, is also provided. Here, the optical sheet is also accommodated between the rear frame and the mold frame as in the light source or the light guiding plate. In addition, the reflection sheet is disposed between the light guiding plate and the rear frame.
Accordingly, in the related planar light source device, the number of components was large. Specifically, the structure of the mold frame was complex and the cost of the mold was very expensive. Therefore, a related art is known for obtaining a cheap and light weight liquid crystal display device where the number of components thereof have been decreased by forming the reflection sheet and removing the mold frame (for example, refer to JP-A-2009-145858, Page 3 to 5, FIG. 1).
In the related art, when the optical member such as an optical sheet or a light guiding plate is provided, the optical member is disposed inside the reflection sheet, which was shaped, instead of the mold frame. For this reason, there is a problem that the positioning operation of the optical sheet is difficult when inserting the optical sheet. In addition, in the insertion operation of the optical sheet, there is also a problem that is called as erroneous insertion caused by the front side and the rear side of the optical sheet are reversed. However, such erroneous insertion of the optical sheet is not described in the JP-A-2009-145858.